Generally, in a receiver for use in wireless communications systems, it is desirable to maximize the strength of a received signal. Maximizing the received signal strength can enhance the performance of the wireless communications system by permitting reception of the transmitted signal (when the received signal strength is at or near a minimal power level) that would otherwise be not be receivable, and increasing the signal-to-noise ratio to improve the overall system performance (data transfer rate or reducing the error rate) of the wireless communications system.
In an ultra-wideband (UWB) wireless communications system that makes use of a stream of short-duration pulses to encode and convey information, the detection and maximization of the signal power of the pulses are generally important to maximize system performance. To maximize the reception of the short-duration pulses, the receiver generally aligns its detector precisely with each short-duration pulse. By precisely aligning the detector with the arrival of each short-duration pulse, the detector has the ability to detect each short-duration pulse for a maximum period of time, hence increasing the amount of each short-duration pulse received. Even small misalignments can result in significant reductions in signal strength. With more signal from each short-duration pulse received, the receiver is in effect maximizing the strength of the received signal.
Due to the fact that the intervals between each pulse can vary (either on purpose or through error), a method of simply precisely detecting a first pulse (or a first few pulses) and then simply using timing information derived from that first pulse to detect the arrival of subsequent pulses does not, in general, provide good results. The interval drift may be a result of reference clock drift at either the transmitter or the receiver or both. Additionally, this technique does not lend itself to the situation wherein the data conveyed in the stream of short-duration pulses is carried in the difference between the actual arrival time of a short-duration pulse and its expected arrival time.
In an attempt to use the arrival of previously received pulses to predict the arrival of subsequent pulses, the receiver can re-synchronize historical timing information with the time of the arrival of a pulse immediately prior to the arrival of the expected pulse to attempt to precisely align the detector with the pulse. This normally yields better performance than using the timing reference of a pulse that arrived a long time ago, but the problems with reference clock drift can still exist as is the problem with UWB communications systems that use pulse arrival time to convey data.
Additionally, a fairly commonly used pulse shape in UWB wireless communications systems is known as a Gaussian pulse. A Gaussian pulse can be described by a mathematical expression:
            p      ⁡              (        t        )              =          Ke              -                              (                          t                              T                s                                      )                    2                      ,where K is a normalization factor and Ts is the Gaussian pulse parameter. While the Gaussian pulses have certain characteristics that favor their use, it can be difficult to create a simple and inexpensive detector to detect Gaussian pulses. To further complicate the issue, the UWB antennas used to transmit and receive the Gaussian pulses may behave like differentiators or integrators (depending upon their implementation) when used in typical UWB frequency ranges. Therefore, the process of detecting the Gaussian pulses (or whatever pulses are being transmitted) is made even more difficult.
One disadvantage of the prior art is that it uses timing information derived from previously arrived pulses to detect the arrival of future pulses. Due to problems associated with clock drift and even modulation schemes that make use of the difference between the actual arrival time of a pulse with its expected arrival time to encode data, the timing information derived from previously arrived pulses may not provide an optimal solution.
A second disadvantage of the prior art is that the attempted detection of the pulse being received results in a detector that is more complex (hence more expensive) than necessary. A simpler design for a detector would result in a lower hardware requirement for the detector and the overall receiver, this will, in turn, result in a less expensive receiver.